Commercially available electrostatic copying machines, or copiers, generally include processing apparatus for forming and developing an electrostatic latent image on a moving photoreceptor and thereafter transferring the developed image from the photoreceptor to a copy sheet made of suitable material such as paper.
As shown in U.S. Pat. No. 3,998,542, issued Dec. 21, 1976 to John A. Toto et al, many of such copiers are provided with well-known means for flash illuminating a document, placed by the operator at the copier's document illuminating station, typically a glass platen, to expose the photoreceptor with light modulated by the graphic information on the document. Whereupon, the photoreceptor selectively conducts to form the electrostatic latent image on the photoreceptor. The light sensitivity of the photoreceptor and intensity of the light utilized for flash illumination purposes are such that the time period required for photoreceptor imaging purposes is on the order of 10 milliseconds or less. It is therefore desirable to equip the copier with a document feeder to permit the operator to take advantage of the rapidity with which copies can be made by avoiding the time-consuming task of carefully locating successive documents at the illuminating station.
One of the long standing problems in the prior art resides in the provision of a simply constructed document feeder which is sufficiently adaptable to reliably handle various documents made of different materials that are of different thickness and diversely calendered. For example, in the course of daily usage of a copier equipped with a document feeder, the feeder may be called upon to handle documents made of plain bond paper, tissue paper or plastic, or the like, of various thicknesses, without folding, creasing, crumpling, or otherwise mutilating, the documents. Accordingly:
An object of the present invention is to provide a simply constructed document feeder for a copier of the type which utilizes flash illuminating means for making copies of a document; and
Another object is to provide such a document feeder for reliably feeding documents of different thickness which are respectively differently calendered.